Binder composition, a method of manufacturing a corrosion-resistant sacrificial protective coating using said composition, and a support coated with such a coating

ABSTRACT

The present disclosure provides an aqueous binder composition for forming a sacrificial corrosion-protective coating, said composition being free of chromates and also preferably free of borates and molybdates. Said binder composition advantageously has a pH of less than 6 and comprises a binder, particles of at least one metal oxide and at least one metallic phosphate, said binder comprising a hydrolyzed organosilane oligomer. In addition, the proportion by weight of said particles of at least one metal oxide relative to the total dry weight of said binder composition is greater than or equal to 75%.

The present disclosure relates to aqueous binder compositions forforming a sacrificial corrosion-resistant protective coating on at leastone surface portion of a support, which compositions are in particularfree of carcinogenic, mutagenic, or reprotoxic compounds also known bythe abbreviation CMR compounds.

BACKGROUND OF THE DISCLOSURE

The present disclosure also relates to methods of manufacturing andapplying sacrificial protective coatings of this type, and to supportscoated thereby.

Conversion treatments lead to a superficial modification of the metallicsupport (alloys of aluminum, titanium, iron and other metals) by ananodizing process (electrolysis operation, for example chromic,sulfuric, or phosphoric anodic oxidation) or by a simple chemicalconversion process (for example chromating or phosphating).

Chromating can be used to form a thin, highly adhesive deposit ofmetallic chromates by bringing the surface of the part to be treated(typically aluminum or zinc alloys or steels) into contact with anacidic solution based on dichromates and fluorinated activating agents.That treatment improves the corrosion resistance of the support and isalso used as a keying base for paints.

However, such processes suffer from the disadvantage of using toxiccompounds, particularly as regards the excess treatment and washingwater used for the treated supports.

Further, the washing water and solutions employed need to be treated toeliminate the heavy dissolved CMR metals before discharging them orreusing them. Eliminating metals produces additional toxic waste, whichis difficult to purify and to treat.

A support, in particular a support including iron and constituting asub-assembly or a component of aircraft equipment, can be provided withsacrificial protection against corrosion, in particular against red rustcorrosion, by applying a moist single- or two-component bindercomposition containing a solvent or dilutable in water, but that suffersfrom numerous constraints. Single-component compositions must bere-dispersed at least 24 hours (h) before they are used. Once suchbinder compositions have been applied to the support that is to befunctionalized, possibly after a first evaporation step, it is necessaryto carry out a first cure, then to allow the support to cool down, andthen to carry out a second cure, known as an anneal, for several hours.A third cure or final cure might be necessary and could last 5 h.

Using such compositions also necessitates intermediate compacting whenintermediate annealing is carried out. That operation consists inspraying particles such as corundum particles onto the portion of thesurface of the support to be functionalized, at a pressure that is from100 kilopascals (kPa) to 150 kPa, the dimensions of said particles beingin the range 90-180 US mesh. A compacting operation known as finalcompacting, which is thus different from the intermediate operation interms of pressure (kPa) and dimensions of the projected particles, isalso carried out in order to finish the coating.

Binder compositions of that type also suffer from the major disadvantageof including trivalent and/or hexavalent chromates as well as borates.

In operation, binder compositions of that type are combined with asacrificial metallic pigmentation, in particular of aluminum or ofmagnesium, these latter being associated with the chromium III or VIcomponents and acting to inhibit corrosion and to passivate the support,as well as acting as the above-mentioned metal pigmentation.

Sacrificial performance, and thus corrosion resistance, can only beobtained after performing the above-mentioned treatment operations ofannealing and of compacting, which operations are awkward and can becarried out with any guarantee of success only by qualified, certifiedoperators.

EP 0 995 816 A1 is known, and discloses a binder composition comprising,in the aqueous phase, phosphate ions and chromium III ions and secondarycationic species such as aluminum ions, zinc ions, or indeed magnesiumions to which metal oxide particles are also added.

That binder composition does away with the use of hexavalent chromium,but still employs chromium III ions.

In addition, US 2006/0225613 is known, which describes the synthesis ofan epoxysilane oligomer that is said to present good stability and gooddispersion in an aqueous medium despite its high molecular weight. Saidorganosilane oligomer is mixed with metallic particles the quantity ofwhich must not exceed 35% by weight of the total binder compositionweight so that the film obtained retains its good appearance (see[0046]). The binder composition examples (4 to 18 and 21) for which thecorrosion properties were tested comprise 28% by weight of zinc oxideand 3% of aluminum oxide. There is no indication as to the appearance ofthe films obtained. In all of those examples, the binder composition isdried at 70° C. for 20 minutes (min) then dried at 300° C. for 30 min inorder to polymerize the organosilane oligomer and form the film ofcorrosion-protective paint. The corrosion resistance test consists inbringing the substrate coated with a film corrosion-protective paintinto contact with a saline solution at a temperature of 35° C. asdefined in accordance with ISO standard 7253:1984. The measured valuecorresponds to the time after which 5% of red rust compared with thetotal weight of the coating appears when the substrate coated with thefilm of corrosion-resistant paint is placed in a stove at 35° C. The redrust corresponds to oxidation of iron contained in the support to beprotected against corrosion, which means that said salt spray passesthrough the film of corrosion-resistant paint, which no longer protectsthe substrate. The above-mentioned standard, which has been updated andnow corresponds to ISO standard 9277-2012, defines the type of saltspray, but it does not define the specifications to be complied with asregards corrosion, nor does it define in precise terms the time forapplication of said salt spray. In US 2006/0225613, after only a fewhours, 5% of red rust relative to the total weight of the coating hasalready been formed. A sacrificial corrosion-protective coating shouldallow red rust to appear only after a few hundred hours, or even morethan 1000 h. Thus, US 2006/0225613 concerns a binder composition for themanufacture of a film of corrosion-resistant paint that is not suitablefor the manufacture of a corrosion-protective coating that issacrificial and that is thus intended to resist extreme corrosiveconditions such as several salt spray cycles, each cycle lasting morethan 15 h and comprising a period during which the coating is exposed totemperatures greater than or equal to 250° C. for several hours.

OBJECT AND SUMMARY OF THE DISCLOSURE

The present disclosure provides an aqueous binder composition for themanufacture of a sacrificial corrosion-protective coating, in particulara primer, having the following properties:

-   -   good adhesion to the support, and with primers and paints that        are subsequently applied as a top coat;    -   good corrosion resistance, in particular sacrificial corrosion        resistance when exposed to a salt spray as defined in French        standard NF EN ISO 9227-2012;    -   good resistance to scratches, chemical products and wear;    -   an electrical surfactant resistivity of 1 ohm/square or less.

The present disclosure also provides a kit for an aqueous bindercomposition that can function without carcinogenic, mutagenic, orreprotoxic compounds, and in particular is free of molybdates and/orchromates and/or borates or heavy metals.

The present disclosure also provides a method of manufacturing asacrificial corrosion-protective coating that is easy to prepare anddoes not require intermediate annealing and compacting operations inorder to obtain a coating that may have a final thickness of 90micrometers (μm).

Thus, in a first aspect, the present disclosure provides an aqueousbinder composition for the manufacture of a sacrificialcorrosion-protective coating, said composition preferably being free ofchromates and also preferably free of borates and molybdates. Saidbinder composition has a pH of less than 6 and comprises a binder,particles of at least one metal oxide, and at least one metallicphosphate, said binder comprising a hydrolyzed organosilane oligomer. Inaddition, the proportion by weight of said particles of at least onemetal oxide relative to the total dry weight of said aqueous bindercomposition is greater than or equal to 75%.

It has been discovered that the combination of a majority of metallicparticles in an aqueous binder composition combined with at least onemetallic phosphate and an organosilane oligomer means that a sacrificialcorrosion-protective coating can be formed with excellent salt spraycorrosion resistance properties, even when it is exposed to cycles attemperature greater than or equal to 250° C., while retaining a coatingwith an appearance that is regular without the formation of blisters orother irregularities.

When the binder composition does not include at least one metallicphosphate, the sacrificial corrosion-protective coating obtained formsblisters after approximately five complete salt spray resistance cyclesand at temperatures of approximately 450° C., each complete cyclelasting 24 h and comprising a first cycle during which the coating isexposed to a temperature of 450° C. for 6 h, followed by a second cycleduring which said coating is left at ambient temperature, then a thirdcycle during which said protective coating is exposed to a salt sprayfor 16 h as defined in ISO standard 9227-2012, and finally a fourthcycle identical to the above-mentioned third cycle.

Without wishing to be limited to any one scientific theory, anon-exhaustive explanation would be that the sacrificial protectivecoating lacks a barrier effect as regards the diffusion of oxygen andmoisture. Once introduced into the sacrificial protective coating,oxygen and moisture are suspected of generating corrosion of the iron bysaid hot coating in the furnace at 450° C., especially when exposed tosalt spray.

Adding at least one metallic phosphate improves the barrier effect ofthe sacrificial protective coating, in particular by densifying thematrix between the metallic particles by means of very good affinitywith the organosilane oligomer. Furthermore, it has also been observedthat the behavior of the sacrificial protective coating in the presenceof at least one metallic phosphate is more reproducible in terms ofelectrochemical activity, even for different coating thicknesses (forexample 25 μm or 50 μm), compared with when the binder composition doesnot include at least one metallic phosphate.

In the context of the present disclosure, the term “dry matter of theaqueous binder composition”, optionally of the part A and/or the part Bas described below, means the residual dry matter once the volatilecompound or compounds has/have evaporated off, in particular those witha boiling point less than or equal to 100° C., in particular water.Preferably, the residual dry matter corresponds to the mass in grams (g)of aqueous binder composition from which the quantity of water itcontains also in grams has been subtracted.

Preferably, part B described below does not include water or a volatilecompound, and so the dry matter of part B corresponds to the totalweight of part B.

Preferably, the particles of metal oxide(s) is/are selected so thattheir galvanic potential(s) millivolts (mV) is/are lower than thegalvanic potential of the metallic surface(s) to be coated. The galvanicpotential can be measured by immersing two different metallic materialsin a saline solution at a predetermined temperature, for example atapproximately 25° C., then measuring the potential difference (mV)obtained between said two materials. Thus, the metal oxide particlesneed to be based on one or more metals that is/are less noble than themetal or metallic alloy of the support to be coated. In the context ofthe present disclosure, the term “metallic phosphate” means any compoundincluding a neutral phosphate ion, such as phosphate PO₄ ³⁻,tripolyphosphate (P₃O₁₀ ⁵⁻¹), or hexametaphosphate (P₆O₈ ⁶⁻), togetherwith one or more metal(s), said metal(s) in particular being selectedfrom zinc, aluminum, manganese, or a mixture thereof. Preferably, thepercentage values indicated in the present text are given to within ±5%concerning the weight of the various components. Preferably, the valuesconcerning the electrical surface resistivity given in the present textare given to within ±10%, more preferably to within ±5%.

In a variation, said at least one metallic phosphate is selected fromthe group constituted by zinc phosphate (Zn₃(PO₄)₂), manganesephosphate, (Mn₃(PO₄)₂), aluminum phosphate (AlPO₄), aluminumtripolyphosphate (Al₅(P₃O₁₀)₃), aluminum and zinc phosphate, andmixtures thereof, preferably from the group constituted by zincphosphate and aluminum tripolyphosphate.

In one embodiment, the proportion by weight of at least one metallicphosphate is more than 0 and less than or equal to 15% relative to thetotal dry weight of said aqueous binder composition, preferably lessthan or equal to 10%, more preferably less than or equal to 8%, inparticular greater than or equal to 3%, relative to the total dry weightof said aqueous binder composition.

In a variation, said at least one metal oxide particle is selected fromthe group constituted by aluminum oxide, zinc oxide, a mixedzinc-magnesium oxide, a mixed aluminum-zinc oxide, and mixtures thereof,preferably from the group constituted by aluminum oxide and a mixedaluminum-zinc oxide.

The mixed aluminum-zinc oxide primarily comprises aluminum by weight,preferably at least approximately ⅔ aluminum for at most ⅓ zinc byweight.

In a variation, the proportion by weight of particles of at least onemetal oxide is greater than or equal to 80%, preferably greater than orequal to 85%, relative to the total dry weight of said aqueous bindercomposition.

In a variation, said organosilane oligomer has the following formula(I), [R₄—(SiR₁R₂R₃)]_(n), in which n is an integer with 2≦n≦100 and R₄is a non-hydrolyzable group and at least one group from R₁, R₂, and R₃is a hydrolyzable group.

Preferably, 2≦n≦75; more preferably 2≦n≦50; 2≦n≦40; in particular2≦n≦25; and especially, 2≦n≦15.

The term “hydrolyzable group” means any group that is capable ofseparating from the silicon atom under the effect of water decomposingto generate H₃O⁺ and OH⁻ ions, in particular under the effect of H₃O⁺ions in the context of the present disclosure, since the pH of theaqueous binder composition is less than 6.

The hydrolyzed organosilane (I) forms a silanol equivalent and analcohol during the first hydrolysis reaction. The organosilane withformula (I) then reacts with the silanol formed and the silanols formedreact with each other during second condensation reactions to formpolysiloxane oligomers or polymers, i.e. containing —Si—O—Si— bridges.

The silanols also react with the metal oxide particles to graft them, inparticular with the hydroxyl functions supported on the surface of saidparticles.

Preferably, said organosilane oligomer is selected from anorganodialkoxysilane oligomer or an organotrialkoxysilane oligomer, morepreferably from an epoxy dialkoxysilane or an epoxytrialkoxysilane or avinyldialkoxysilane or a vinyltrialkoxysilane.

The organosilane oligomer according to embodiments of the presentdisclosure comprises a non-hydrolyzable group R₄ and at least onehydrolyzable group selected from R₁, R₂ or R₃, which groups,independently of each other, are either in the structure per se, i.e. inthe carbon chain, of the organosilane oligomer, for example at the endof the chain, or are branches attached to said chain at regularintervals.

In a variation, R₄ and optionally R₁ and/or R₂ and/or R₃ when it/theyrepresent(s) one or more non-hydrolyzable groups independently of eachother, represent a group selected from: a C₁-C₂₀ alkyl group or C₃-C₁₀cycloalkyl group substituted with one or more epoxy group(s), said epoxygroup being mono, di, tri, or tetravalent; a glycidoxy group; a C₁-C₂₀alkyl group substituted with a glycidoxy group; a vinyl group (CH₂═CH—);a C₁-C₂₀ alkyl group substituted with a vinyl group (CH₂═CH—); a C₁-C₂₀alkyl group substituted with a primary amine and/or a secondary amineand/or a tertiary amine; a primary amine; a secondary amine; a tertiaryamine; a C₁-C₂₀ alkyl group substituted with a thiol group; a thiolgroup; a urea group; a C₁-C₂₀ alkyl group substituted with a urea group;an isocyanate group; and a C₁-C₂₀ alkyl group substituted with anisocyanate group.

Further, at least one group selected from R₁, R₂, and R₃ presents as itshydrolyzable group: a C₁-C₁₀ alkoxy group; a C₃-C₁₀ cycloalkyloxy group;a C₅-C₁₀ aryloxy group or a C₁-C₅ acyloxy group.

Said above-mentioned alkyl groups, whether for the hydrolyzable group orthe non-hydrolyzable group, are C₁-C₂₀, preferably C₁-C₁₅, morepreferably C₁-C₁₀, which are saturated, linear, or branched, and thecycloalkyl groups are saturated, preferably C₃-C₆.

In the context of the present disclosure, when a group is said to beC_(n)-C_(p) (also termed C_(n) to C_(p)), this means that it has n to pcarbon atoms, n and p being integers.

Examples of monovalent epoxy groups are the glycidoxy group,—O—CH₂—C₂H₃O, or the R—C₂H₃O (or Ri-oxirane) group in which R_(i) is alinear or branched alkyl chain, which may optionally be saturated, acycloalkyl, an alkenyl, an aryl, an ether, or a polyether. Theabove-mentioned alkyl chains are preferably C₁ to C₁₀, and theabove-mentioned cycloalkyls are preferably C₃ to C₁₀, more preferably C₃to C₆.

Examples of the divalent epoxy groups are as follows:-(-)C(—O—)CR_(ii)R_(iii) and —CR_(ii)(—O—)CR_(iii)—; examples oftrivalent epoxy groups are as follows: -(-)C(—O—)CR_(ii); examples oftetravalent epoxy groups are as follows: -(-)C(—O—)C(-), in which R_(ii)and R_(iii), independently of each other, are a structure selected fromthose listed above for R_(i).

Preferably, the quantity of epoxy function of the oligomer with formula(I), i.e. with an oxirane function, is less than or equal to 15millimoles per gram (mmoles/g) of organosilane oligomer, preferably lessthan or equal to 10 mmoles/g of organosilane oligomer, and morepreferably less than or equal to 4.75 mmoles/g of organosilane oligomer.

In the context of the present disclosure, the term “alkoxy group” meansany group with formula R_(a)—O in which R_(a) represents a linear orbranched saturated alkyl group optionally including an —OH function,preferably C₁ to C₁₀, more preferably C₁ to C₆, still more preferably C₁to C₄, examples of which are the methoxy, ethoxy, isopropoxy, n-propoxy,i-propoxy, n-butoxy, i-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, andn-hexyloxy groups.

In the context of the present disclosure, the term “cycloalkyloxy group”means any group with formula R_(b)—O in which R_(b) represents acycloalkyl group, preferably C₃ to C₁₀, such as the cyclopropyloxy orcyclohexyloxy groups.

In the context of the present disclosure, the term “cycloalkyl group”means any cyclic alkyl group, preferably C₃ to C₁₀, for example thecyclohexyl or cyclopropyl group.

In the context of the present disclosure, the term “aryloxy group” meansany group with formula R_(c)—O in which R_(c) represents an aryl group,preferably C₅ to C₁₀, such as the phenoxy group, for example.

In the context of the present disclosure, the term “aryl group” meansone or more aromatic rings advantageously containing 5 to 10 carbonatoms, which may be coupled or fused. In particular, the aryl groups maybe monocyclic or bicyclic groups, preferably the phenyl group.

In the context of the present disclosure, the term “acyloxy group” meansany group with formula R_(d)—CO—O in which R_(d) represents a saturatedlinear or branched alkyl group, preferably C₁ to C₄, such as acetoxy orpropionyloxy groups.

Alkoxy groups, in particular the methoxy, ethoxy, and isopropoxy groups,are preferred hydrolyzable groups.

In the context of the present disclosure, the term “primary amine” meansany group with formula R_(e)NH₂, the term “secondary amine” means anygroup with formula R_(e)R_(f)NH, and the term “tertiary amine” means anygroup with formula R_(e)R_(f)R_(g)N, in which R_(e), R_(f) and R_(g) arelinear or branched alkyl groups, which may optionally be saturated,preferably C₁ to C₂₀, or more preferably C₁ to C₁₀, and still morepreferably C₁ to C₄.

In the context of the present disclosure, the term “thiol group” meansany group with formula R_(h)—SH in which R_(h) is a linear or branchedalkyl group, which may optionally be saturated, preferably C₁ to C₂₀,more preferably C₁ to C₁₀, and still more preferably C₁ to C₄.

In the context of the present disclosure, the term “urea group” meansany group with formula (R_(i), R_(j))N—C(═O)—N(R_(k),R_(l)) in whichR_(i), R_(j), R_(k) and R_(l), independently of one another, are ahydrogen atom or a linear or branched alkyl group, which may optionallybe saturated, preferably C₁ to C₂₀, more preferably C₁ to C₁₀, and stillmore preferably C₁ to C₄.

In the context of the present disclosure, the term “isocyanate group”means any group with formula R_(m)—N═C═O, in which R_(m) is a hydrogenatom or a linear or branched alkyl group, which may optionally besaturated, preferably C₁ to C₂₀, more preferably C₁ to C₁₀, and stillmore preferably C₁ to C₄.

In the context of the present disclosure, the term “alkenyl group” meansany group with formula R_(o)R_(p)C═CR_(r)R_(s) in which R_(o), R_(p),R_(r), R_(s) R_(l), independently of one another, are a hydrogen atom ora linear or branched alkyl chain, which may optionally be saturated,preferably C₁ to C₂₀, more preferably C₁ to C₁₀, and still morepreferably C₁ to C₄, such as a vinyl group, for example.

In a variation, R₁ and/or R₂ and/or R₃, preferably R₁ and R₂, R₂ and R₃or R₁ and R₃, more preferably R₁, R₂ and R₃, represent an alkoxy group,a cycloalkoxy group, an aryloxy group or an acyloxy group, preferably aC₁-C₆ alkoxy group.

In a variation, R₄ is an alkyl group substituted with an epoxy group,preferably glycidoxy, with formula X-Y- attached to the silicon atom, inwhich X is a glycidoxy group, —O—CH₂—C₂H₃O; or oxirane; and Y is a groupselected from: —(CH₂)_(n)—, with 1≦n≦12, more preferably with 1≦n≦6; anda group comprising a C₃-C₆ cycloalkyl group.

In a variation, the alkoxy group is selected from the following groups:methoxy, ethoxy, propoxy, isopropoxy, isobutoxy, acetoxy, methoxyethoxy,monovalent alkoxy groups derived from diols comprising an alcohol and analkoxy group selected from —O—CH₂CH₂—OH, such as ethyleneglycol;propyleneglycol; neopentyl glycol; 1,3-propanediol;2-methyl-1,3-propanediol; 1,3-butanediol; 2-methyl-2,4-pentanediol;1,4-butanediol; cyclohexane dimethanol; or picanol, preferably from thegroups methoxy; ethoxy; propoxy; and isopropoxy.

In a variation, the motif R₄—(SiR₁R₂R₃) of the organosilane oligomerwith formula (I) is selected from a list (IIa):gamma-glycidoxypropyltrimethoxysilane;gamma-glycidoxypropyltriethoxysilane; gamma-glycidoxypropylmethyldimethoxysilane; and gamma-glycidoxypropylmethyldiethoxysilane;and from a list (IIb): beta-(3,4-epoxycyclohexyl)-ethyltrimethoxysiloxane; beta-(3,4-epoxycyclohexyl)-ethyl methyldimethoxysilane, beta-(3,4-epoxycyclohexyl)-ethyl methyl diethoxysilane;and beta-(3,4-epoxycyclohexyl)-ethyl triethoxysilane, preferably fromlist (IIa).

Preferably, the general formula for the organosilane oligomer compoundaccording to embodiments of the present disclosure is(C_(x)H_(y)O_(z)Si)_(n) with 4≦x≦20, more preferably x≦15, and morepreferably x≦10, with 15y≦30, and z≧2, more preferably z≧4, and morepreferably z≦6, n being an integer with 2≦n≦100.

The choice of organosilane oligomer is important so that a film can beformed on the support to be protected in which the metal oxide particlesinteract with the silicon atoms and form an organized matrix once thecomponents based on carbon and oxygen have been destroyed by heating asis described below.

In a variation, the hydrolyzed organosilane oligomer represents in therange 5% to 30% by weight of the total dry weight of said aqueous bindercomposition, preferably in the range 5% to 15% by weight of the totaldry weight of said aqueous composition, more preferably in the range 5%to 10% by weight of the total weight of said aqueous binder composition.

In a variation, the aqueous binder composition comprises an acidiccatalyst selected from the group constituted by p-toluene sulfonic acid,phosphoric acid, boric acid, acetic acid, and mixtures thereof,preferably from the group constituted by p-toluene sulfonic acid, aceticacid and phosphoric acid; more preferably, the catalyst is p-toluenesulfonic acid.

This catalyst can be used to initiate the polymerization reaction byself-condensation, which is activated by heating, in particular duringdrying (iii) and especially during the intermediate (v) or final (vi)annealing step, which are described below.

Preferably, the ratio of the number of moles/liter of acidic catalyst tothat of the organosilane compound with formula (I) is in the range 1/60to 1/5, more preferably in the range 1/40 to 1/20.

In a variation, the particles of at least one metal oxide have agranulometric distribution for 10% to 90% by weight of said particles inthe range 2 μm to 30 μm; preferably, said particles are spherical.

The grain size is measured by the dry or wet method using a lasergranulometer such as that marketed by MALVERN, for example theMASTERSIZER 3000® or 2000®.

In a second aspect, the present disclosure provides a kit for an aqueousbinder composition in accordance with any one of the precedingembodiments, said kit comprising a part A having a pH of less than 6constituted by an aqueous composition comprising a hydrolyzedorganosilane oligomer and a part B comprising particles of at least onemetal oxide and at least one metallic phosphate, the proportion byweight of particles of at least one metal oxide relative to the totaldry weight of parts A and B added together being greater than or equalto 75%.

Preferably, the proportion by weight of the particles of said at leastone metal oxide relative to the total dry weight of part B and theproportion by weight of the dry matter of part B relative to the totaldry weight of part A are determined such that the proportion by weightof particles of at least one metal oxide relative to the total dryweight of parts A and B added together is greater than or equal to 75%.

The hydrolyzed organosilane oligomer of part A corresponds to theorganosilane oligomer described above, in particular to that withformula (I) described above and in accordance with all of theembodiments described above with reference to the first aspect.

The particles of at least one metal oxide for any one of the variantembodiments described above are in accordance with the first aspect.

Said at least one metallic phosphate for any one of the variantembodiments described above are in accordance with the first aspect.

In a variation, the organosilane oligomer hydrolyzate represents in therange 5% to 50% by weight, preferably in the range 5% to 30% by weightrelative to the total dry weight of part A.

In a third aspect, the present disclosure also provides the use of theaqueous binder composition in accordance with any one of the variantembodiments described or of the kit as described above to form asacrificial corrosion-protective coating on at least a portion of thesurface of a support, in particular a support formed from a materialselected from metals, metal alloys and composite materials comprising ametal or a metal alloy, preferably with an electrical surfaceresistivity of less than 1 ohm/square.

Advantageously, said surface portion of the support has a galvanicpotential (mV) that is higher than the galvanic potential (mV) of themetallic particles that comprise said coating.

In general, said support is any metallic element that is exposed tosevere wear conditions, for example: an engine or generator turbineshaft, an axle on road or railroad rolling stock, a power or motiontransmission shaft, wind turbine ball bearings, a metal part foroffshore construction, or a particular element for an aircraft.

Preferably, said sacrificial protective coating has an electricalsurface resistivity of less than 1 ohm/square.

The resistivity indicated above corresponds to the indicated surfaceresistivity when the thickness of the coating for which the resistivityis being measured is considered to be negligible.

Preferably, the sacrificial corrosion-protective coating according toembodiments of the present disclosure has a thickness greater than orequal to 20 μm and less than or equal to 120 μm, more preferably greaterthan or equal to 40 μm, more particularly less than or equal to 90 μm,in particular less than or equal to 60 μm, in the dry state, inparticular after the final annealing step and/or the final compactingstep.

In accordance with a fourth aspect, the present disclosure provides amethod of manufacturing and applying a sacrificial corrosion-protectivecoating to at least one surface portion of a support using the aqueousbinder composition described in accordance with any one of the precedingvariant embodiments, comprising the following steps in succession:

(i) a step of supplying and preparing at least one surface portion of asupport formed from metal or a metal alloy;

(ii) a step of applying the aqueous binder composition according to anyone of the preceding variant embodiments in order to form a moist layerof film on at least said surface portion;

(iii) a drying step to evaporate the water and allow a film to be formedat a temperature in the range 60° C. to 90° C. for at least 5 min;

(iv) optionally, repeating steps (ii) and (iii) until a film with apredetermined thickness is obtained;

(v) optionally, after each drying step (iii) with the exception of thelast drying step (iii), a step of intermediate annealing and/or a stepof intermediate compacting of the film is/are applied;

(vi) a final step of annealing said film obtained at the end of step(iii) at a temperature greater than or equal to 250° C. for at least 30min;

(vii) a step of final compacting of said at least one surface portioncoated with said sacrificial corrosion-protective film so as to form asacrificial corrosion-protective coating, preferably with an electricalsurface resistivity of less than 1 ohm/square.

Advantageously, the compacting step acts to work harden the sacrificialcorrosion-protective coating.

The final annealing step (vi) and the final compacting step (vii) arecarried out on the film after the last drying step (iii) applied to saidfilm, and so an intermediate annealing step or an intermediatecompacting step are not carried out, as they would be redundant in thelight of the corresponding final steps.

Preferably, each compacting step, whether it is intermediate or final,comprises blasting a powder such as corundum (Al₂O₃) of grain size thatis preferably in the range 80 to 200 US mesh, more preferably in therange 80 to 180 US mesh, at a pressure greater than or equal to 100 kPa,preferably greater than or equal to 200 kPa.

It has been discovered that the combination of an aqueous bindercomposition mainly comprising particles of at least one metal oxide inthe presence of at least one metallic phosphate, and a hydrolyzedorganosilane oligomer undergoing an appropriate final annealing stepcombined with a final compacting step can be used to form a sacrificialcorrosion-protective coating with an electrical surface resistivity ofless than 1 ohm/square, and has excellent corrosion resistance over timeand at high temperatures without using chromates, molybdates, or evenborates, and while preserving a good appearance.

Advantageously, an intermediate annealing step and/or an intermediatecompacting step is/are not essential in order to form a sacrificialcorrosion-protective coating that is satisfactory compared with theprior art. In fact, using a binder composition in accordance withembodiments of the present disclosure means that steps (ii) and (iii)can be carried out in succession as many times as is necessary to obtaina moist film with the desired thickness, then a final annealing stepfollowed by a final compacting step can be carried out directly withouthaving to carry out an intermediate annealing and/or intermediatecompacting.

Advantageously, it is possible to deposit the layer of bindercomposition according to embodiments of the present disclosure in asingle layer of moist film with a thickness that may be up to 140 μm,which corresponds to a finished and thus dry sacrificial protectivecoating of the order of 90 μm. In the prior art, it is necessary toapply several layers of binder compositions then to dry them andpossibly to carry out intermediate annealing steps and/or intermediatecompacting steps in order to obtain this thickness of 90 μm on thefinished coating.

This arrangement represents substantial time and cost savings of themethod of the present disclosure compared with the prior art methods.

Preferably, the temperature (° C.) and the period during which theannealing step is applied are determined so that said sacrificialcorrosion-protective coating comprises, relative to its total weight,less than 10% by weight, preferably less than 5% by weight of ahydrocarbon residue.

Preferably, the application step (ii) comprises a step of spraying orsprinkling the pigmented aqueous binder composition according toembodiments of the present disclosure, more preferably a spraying step.

Preferably, the drying step (iii) comprises exposing the support to atemperature in the range 80° C. to 90° C. for at least 5 min, morepreferably for at least 20 min and at most 10 h, preferably at most 2 h.

Preferably, the final annealing (vi) or intermediate annealing (v) stepis carried out at a temperature greater than or equal to 250° C., inparticular at less than or equal to 500° C., more preferably at greaterthan or equal to 285° C., and in particular less than or equal to 480°C., for at least thirty minutes, preferably at least 45 min, morepreferably at least 2 h, still more preferably at least 15 h, still morepreferably at most 24 h, in particular at most 20 h.

Preferably, if the temperature is greater than or equal to 400° C., thefiring time is greater than or equal to 3 h, preferably greater than orequal to 4 h. If the temperature is less than or equal to 300° C., forexample less than or equal to 285° C., the annealing time is greaterthan or equal to 10 h, more preferably greater than or equal to 15 h,more particularly greater than or equal to 20 h.

This step can be used firstly in order to polymerize the organosilaneoligomer hydrolyzate and to distribute the metal oxide particleshomogeneously relative to the silicon atoms, creating bridges betweenthe silica and said particles, then secondly, the components comprisingoxygen and carbon in particular are degraded—carbonized—in order to forma coating mainly comprising silica organized with the metallic particlesin the thickness of said coating. Preferably, this step can be used toform a coating comprising metallic particles and silica, and less than10% by weight, preferably less than 5% by weight of a hydrocarbonresidue in particular obtained from the degradation of said hydrocarbonoligomer, said coating preferably being free from chromium compounds,more preferably free from borates and molybdates.

Thus, at least 90% of the weight of said coating, preferably at least95% of its weight, is comprised by metallic particles, in particularparticles of aluminum and/or zinc and/or magnesium, preferably aluminumand/or zinc.

In a variation, the preparation step (i) comprises a step of sandingsaid at least one surface portion such that said surface portion has arough surface, preferably with a surface roughness of less than 100 μm,and more than 1 μm, more preferably in the range 2 μm to 3 μm.

The surface roughness can be measured in accordance with NF EN ISOstandard 8503 dated April 2012.

Preferably, the sanding step comprises blasting particles, in particularcorundum, with a grain size of 120 US mesh or less, preferably 100 USmesh or less, and more preferably 80 US mesh or less, at a pressure of200 kPa or more, more preferably 300 kPa or more.

In a variation, the pH of the aqueous binder composition applied to thesubstrate during step (ii) is adjusted to between 2 and 4, preferably ata temperature in the range 15° C. to 40° C., and more preferably at atemperature in the range 15° C. to 30° C., more particularly in therange 20° C. to 30° C.

In a variation, the pH is adjusted with the aid of an acid selected fromthe group constituted by p-toluene sulfonic acid, phosphoric acid, boricacid, acetic acid, and mixtures thereof, preferably p-toluene sulfonicacid, phosphoric acid, and acetic acid; more preferably p-toluenesulfonic acid (p-TSA).

In a variation, the pigmentation step consisting in adding particles ofat least one metal oxide to the aqueous binder composition and at leastone metallic phosphate, in particular in the form of a metallic powderso as to obtain the pigmented binder composition used in step (ii), iscarried out with stirring for at least one minute, preferably for atleast 15 min with stirring, more preferably at least 30 min withstirring, at a temperature in the range 15° C. to 40° C., preferably inthe range 15° C. to 30° C., more particularly in the range 20° C. to 30°C.

In a variation, the step of application of the binder composition (ii)comprises spraying said composition onto said at least one surfaceportion of the support so as to form a layer of a film, in the moistcondition, with a thickness greater than or equal to 25 μm and less thanor equal to 200 μm, preferably greater than or equal to 30 μm and lessthan or equal to 185 μm, more preferably greater than or equal to 60 μm,more particularly less than or equal to 140 μm.

The thickness can be measured using NF EN ISO standard 2808, for examplewith the aid of an instrument marketed under the trade name POSITECTOR6000® using the principles of magnetic currents and eddy currents tomeasure the thickness of the coating on ferrous and non-ferrous metals.

In a variation, the application step (ii) is carried out at the earliest30 min after the pigmentation step consisting in adding the particles ofat least one metal oxide and at least one metallic phosphate to theaqueous composition, in particular zinc phosphate or aluminumtripolyphosphate.

In a fifth aspect, the present disclosure provides a support formed froma material selected from metals, metal alloys and composite materialscomprising a metal or a metal alloy, preferably formed from iron and analloy comprising iron, with at least a portion of a surface being coatedwith a sacrificial corrosion-protective coating obtained by carrying outthe method in accordance with any of the variant embodiments describedabove and comprising metallic particles, phosphorus and silica, and lessthan 10% by weight relative to its total weight, preferably less than 5%by weight relative to its total weight of a hydrocarbon residue, saidcoating preferably being free of chromium compounds, more preferablybeing free of borates and molybdates.

In the context of the present disclosure, the term “hydrocarbon residue”means any residue comprising carbon and oxygen.

In a variation, the coating has an electrical surface resistivity ofless than 1 ohm/square.

In the context of the present disclosure, the electrical resistivity maybe measured using a multimeter, or again in accordance with ASTMstandard D 257-07 dated 2007 and entitled “Standard test methods of DCresistance or conductance of insulating materials”. Preferably, 1 squareis of the order of 2.6 square centimeters (cm²).

The electrical surface resistivity of a sacrificial corrosion-protectivecoating is determined by measuring the capacity of said coating toconduct an electric current. Its reciprocal corresponds to theconductivity (=1/resistivity). When the measured resistivity is low,said coating is a good electrical conductor. In contrast, when itsresistivity is high, the coating is a good electrical insulator.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention can be better understood from the followingnon-limiting exemplary embodiments.

I- Examples of Formulations for a Binder Composition in Accordance withEmbodiments of the Present Disclosure Comprising at Least One MetallicPhosphate Example 1

Preparation of Part A of a kit according to embodiments of the presentdisclosure starting from the following compounds:

an organosilane oligomer derived fromgamma-glycidoxypropyltrimethoxysilane (C₉H₂₀O₅Si): in the range 20 g to40 g;

demineralized water: in the range 60 milliliters (mL) to 80 mL.

The pH of part A was adjusted to in the range 2 to 3 with the aid ofp-TSA acid.

Preparation of part B of the kit according to embodiments of the presentdisclosure starting from the following compounds:

metal oxide powder based on aluminum with or without zinc: in the range5 g to 65 g;

zinc phosphate.

In the range 25 g to 45 g of part A was mixed with part B to form anaqueous binder composition. The proportion by weight of particles of atleast one metal oxide in the mixture of parts A and B was greater thanor equal to 75% relative to the total dry weight of the aqueouscomposition. The proportion by weight of said zinc phosphate relative tothe total dry weight of the aqueous composition was in the range 3% to8%, limits included.

After pigmentation of part A, the pH was again adjusted; in thisparticular example, the pH was in the range 2 to 3.

Example 2 was strictly identical to Example 1, with the exception thatthe zinc phosphate was replaced by aluminum tripolyphosphate.

Example 3

Preparation of part A of a kit according to embodiments of the presentdisclosure starting from the following compounds:

an organosilane oligomer derived from trimethoxyvinylsilane (C₅H₁₂O₃Si):in the range 10 g to 30 g;

demineralized water: in the range 60 mL to 80 mL.

The pH of part A was adjusted to between 2 and 3 with the aid of p-TSAacid.

Preparation of part B of the kit according to embodiments of the presentdisclosure starting from the following compounds:

metal oxide powder based on aluminum with or without zinc: 45 -65 g;

zinc phosphate.

In the range 35 g to 55 g of part A was mixed with part B. Theproportion by weight of particles of at least one metal oxide in themixture of parts A and B was greater than or equal to 75% relative tothe total dry weight of the aqueous composition. The proportion byweight of said zinc phosphate relative to the total dry weight of theaqueous composition was in the range 3% to 8%, limits included.

After pigmentation of part A, the pH was again adjusted; in this preciseexample, the pH was in the range 2 to 3.

Example 4 was strictly identical to Example 3, with the exception thatthe zinc phosphate was replaced by aluminum tripolyphosphate.

II- Preparation of a Control Support Using a Prior Art Method

The surface of a steel support was coated with a sacrificialcorrosion-protective coating by carrying out a prior art chromatingmethod, in particular based on chromium VI. The support obtained wastermed a prior art control.

This support initially underwent a first step of preparing its surface;in particular, the surface was degreased with a basic degreaser such asthat marketed by Henkel with reference TURCO 5948 DMP.

The surface was then rinsed with demineralized water and dried with anair blower. The surface was thus ready for sanding, in particular usingparticles of white corundum with a grain size of the order of 80 μm at aspray pressure for said particles of the order of 300 kPa in order toobtain a surface roughness of 2 μm to 3 μm thickness.

The prior art aqueous binder composition was stirred for 24 h beforeuse, then filtered through a stainless steel screen with openings of theorder of 0.025 millimeters (mm). The composition was stirred again justbefore it was applied in two successive layers. The mean thickness of acompacted layer was thus 25 μm. The support coated with a layer ofbinder composition was dried at a temperature of 80° C. for 15 min. Thelayer then changed from a green color to a gray color. The maximum timebetween this drying step and the annealing step was a maximum of 30 min.Thus, almost immediately after drying, the coated support was exposed toan intermediate annealing operation at 285° C. for a minimum of 3 h foreach applied layer (intermediate annealing after application of eachlayer) or at 215° C. for a minimum of 20 h if the support had beencadmium-coated or 285° C. for 5 h for a final anneal. Each layer wascompacted during an intermediate or final compacting step by blastingcorundum with dimensions in the range 90-180 US mesh and applying apressure of 1 kPa to 150 kPa.

III- Preparation of a Steel Support Using the Method Described Below,and Examples 1 to 4 of Pigmented Binder Compositions Described inParagraph I

A steel support was prepared by carrying out the same operations as forthe control support: the only difference was that different sandingoperation parameters were used in which the particles were blasted at apressure of 300 kPa to 400 kPa and had larger dimensions, since theywere less than or equal to 80 US mesh. Furthermore, no intermediateannealing step and no intermediate compacting steps were carried out.

Activated part A from any one of Examples 1 to 4, i.e. with a pH in therange 2 to 3, was then mixed with a metallic paste (part B from any oneof Examples 1 to 4) for 20 min to form an activated aqueous bindercomposition in accordance with any one of Examples 1 to 4, which wasthen filtered through a screen with openings of the order of 0.12 mm.

The activated and pigmented binder composition of Examples 1 to 4 wasstirred just before it was applied. The binder composition of any one ofExamples 1 to 4 was applied in a single layer of moist film, for example25 μm to 200 μm thick, depending on the low pressure pneumatic sprayspecifications, i.e., preferably at a pressure in the range 150 kPa to200 kPa, in 2 to 6 crossed layers.

For complex parts, it is possible to apply the binder composition in aplurality of layers.

The coated support then underwent a drying step (ii) or stoving stepduring which it was exposed, for example, to a temperature of the orderof 90° C. for at least 60 min in order to change the color of the layerfrom dark gray to pale gray.

The coated support then underwent a final annealing step (vi) duringwhich it was exposed to a temperature of 420° C. for 4 h or 285° C. for20 h. The coating formed at the surface of the support was finallycompacted during the final compacting step (vii) by spraying corundumwith dimensions in the range 80 to 180 US mesh, limits included, at apressure of approximately 200 kPa or more.

Table I below summarizes the results of the tests carried out on thesupport obtained in accordance with the method described above inparagraph III; the results were the same for all of the aqueous bindercompositions.

TABLE 1 TESTS STANDARDS REQUIREMENTS RESULTS Application Continuous andContinuous and uniform uniform visual visual appearance appearance Finalthickness NF EN ISO 2808 25 μm to 90 μm 25 μm to 90 μm Corrosion, NF ISO1000 h The red rust appeared in appearance of 9227-2012 the damaged testcoatings red rust after more than 1200 h. With no damage, the red rustappeared after more than 2500 h Adhesion NF ISO 2409 Class 0 or 1 Class0 Hardness NF ISO 1518 >2500 g before >2500 g before immersion immersionBehavior as NF ISO 2409 Specific to each Skydrol: regards NF ISO 1518fluid Class 0 contaminants >2400 g after immersion Behavior - NF ISO2409 10 cycles After 10 cycles moisture NF ISO 1518 Adhesion: class 0Hardness: >2400 g Behavior - NF ISO 2409 100 cycles After 100 cyclestemperature NF ISO 1518 Adhesion: class 0 variations Hardness: >2400 gTemperature NF ISO 20 (A) cycles No blisters were formed corrosion9227-2012 25 (B) cycles on test specimens, nor red 20 (C) cycles rust,since the test coatings remained intact. Conductivity ASTM Standard R <15 Ohms/ R < 1 Ohm/square test D 257-07 (2007): square “Standard TestMethod for DC resistance or conductance of insulating materials”. 20 (A)cycles, where each cycle (A) comprised, in succession: a first cycle of6 h at 450° C., a second cycle of 1 h remaining in a vessel held at 35°C., a third cycle of 16 h under salt spray, a fourth cycle identical tothe third cycle. 25 (B) cycles, where each cycle (B) was identical tocycle (A) with the exception that the temperature of the first cycle was400° C. 20 (C) cycles, where each cycle (C) was identical to cycle (A)with the exception that the temperature of the first cycle was 550° C.Concerning corrosion to form red rust, the tests were carried out insalt spray on specimens with or without damage, the damage being ascratch in the form of a cross made in the coating to be tested, whichcoating had thickness in the range 40 μm to 60 μm. The salt spray andits conditions for application are defined in ISO standard 9227-2012.

IV - Comparative Examples of Aqueous Binder Compositions WithoutMetallic Phosphate

Two binder compositions with references 5 and 6, respectivelycorresponding to the binder composition examples 1 and 2, were prepared,each time without metallic phosphate.

Concerning the corrosion test until red rust appeared, red rust wasobserved to appear in the damage at approximately 500 h. Without damage,red rust only appeared at approximately 1000 h. These results wereobtained for the two binder compositions 5 and 6.

Concerning the temperature corrosion test, the formation of blisters wasobserved after 5 cycles in the three cases (A), (B) and (C) for bothbinder compositions 5 and 6.

In conclusion, adding at least one metallic phosphate, in particularzinc phosphate or aluminum tripolyphosphate, can double the salt sprayresistance of the coating according to embodiments of the presentdisclosure including damage in comparison with coatings that are free ofmetallic phosphate.

With no scratching of the specimens, after 2500 h of exposure to saltspray, the test specimens exhibited neither pitting linked to corrosion,nor blisters. Adding at least one metallic phosphate, in particular zincphosphate or aluminum tripolyphosphate, thus doubled the salt sprayresistance of the undamaged sacrificial protective coatings according toembodiments of the present disclosure.

Adding at least one metallic phosphate, in particular zinc phosphate oraluminum tripolyphosphate, can thus very significantly improve theelectrochemical activity of the sacrificial corrosion-protective coatingas well as the salt spray and temperature corrosion resistance.

Prepared samples as described in paragraph III and comprising bindercomposition 5 exemplified above were tested at various stages of themethod of the present disclosure:

1) sample 1, heat treatment 1 h at 90° C., corresponding to theevaporation step (v);

2) sample 2, 1 h at 90° C. then 4 h at 420° C., corresponding to steps(v) and (vi);

3) sample 3, 1 h at 90° C. then 4 h at 420° C., corresponding to steps(v) and (vi) followed by compacting at a pressure of 4 (metric) tonnes(t) for 1 min.

Analysis of samples 1-3 was carried out with a MagiX wavelengthdispersion X-ray fluorescence spectrometer from Philips.

In order to carry out X-ray fluorescence analysis, the samples need tobe compacted, either pure or with a binder, and the total mass of thepellet must be 200 milligrams (mg) for 13 mm diameter pellets. The threesamples were thus each prepared by mixing 100 mg of the example bindercomposition to be analyzed with 100 mg of boric acid. Each mixture wasthen compacted under a pressure of 4 t for 1 min in order to obtain 13mm diameter pellets. Analysis of these pellets was carried out undervacuum (5 Pascals).

The results of the semi-quantitative analyses are indicated in Table 2below. They are expressed as the percentages by weight. The method canbe used to detect elements from boron to uranium. However, given thatthe presence of boric acid means that oxygen cannot be assayed and inthe light of the nature of the samples (metallic appearance), theresults are presented without the oxygen values. Carbon was detected insample 1, but no signal was observed in the other two samples 2 and 3.

Conversion of the pigmented binder composition was close to 100% sinceno carbon was detected using X-ray fluorescence in the films aftercuring (step (v)).

If one of the binder compositions 1 to 4 had been tested, Table 2 wouldhave shown the phosphorus and the metal obtained from said at least onemetallic phosphate, in particular zinc or aluminum, which would havebeen added to the metallic particles.

TABLE 2 C Al Si Zn Sample 1 Concentrations 15.5 81.9 2.33 0.02 Sample 2Concentrations — 97.2 2.43 0.02 Sample 3 Concentrations — 97.4 2.14 0.07

Advantageously, the combination of the method of the present disclosureand the binder composition according to embodiments of the presentdisclosure means that a sacrificial corrosion-protective coating can beformed in which the matrix is essentially formed by silica, metallicparticles, and at least one metallic phosphate having high-temperaturecorrosion resistance properties (at 400° C. or higher) and salt spraycorrosion resistance properties as defined in ISO standard 9227 with orwithout damage being present, which properties are doubled compared witha sacrificial protective coating that is free of at least one metallicphosphate.

Where any standards of national, international, or other standards bodyare referenced (e.g., ISO, NF, etc.), such references are intended torefer to the standard as defined by the national or internationalstandards body as of the priority date of the present specification. Anysubsequent substantive changes to such standards are not intended tomodify the scope and/or definitions of the present disclosure and/orclaims.

Although the present disclosure herein has been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. The true scope of the disclosure is indicated by thefollowing claims.

1. An aqueous binder composition for manufacturing a sacrificialcorrosion-protective coating, said composition being free of chromatesand also preferably free of borates and molybdates, wherein said bindercomposition has a pH of less than 6 and comprises a binder, particles ofat least one metal oxide and at least one metallic phosphate, saidbinder comprising a hydrolyzed organosilane oligomer, and wherein theproportion by weight of said particles of at least one metal oxiderelative to the total dry weight of said aqueous binder composition isgreater than or equal to 75%.
 2. A binder composition according to claim1, wherein said at least one metallic phosphate is selected from thegroup constituted by zinc phosphate (Zn₃(PO₄)₂), manganese phosphate(Mn₃(PO₄)₂), aluminum phosphate (AlPO₄), aluminum tripolyphosphate(Al₅(P₃O₁₀)₃), aluminum and zinc phosphate, and mixtures thereof.
 3. Abinder composition according to claim 1, wherein said at least one metaloxide particle is selected from the group constituted by aluminum oxide,zinc oxide, a mixed zinc-magnesium oxide, a mixed aluminum-zinc oxide,and mixtures thereof.
 4. A binder composition according to claim 1,wherein the proportion by weight of particles of at least one metaloxide is greater than or equal to 80% relative to the total dry weightof said aqueous binder composition.
 5. A binder composition according toclaim 1, wherein said organosilane oligomer has the following formula(I), [R₄—(SiR₁R₂R₃)]_(n), in which n is an integer with 2≦n≦100 and R4is a non-hydrolyzable group, and at least one group from R1, R2, and R3is a hydrolyzable group.
 6. A binder composition according to claim 5,wherein R4 and optionally R1 and/or R2 and/or R3 when it/theyrepresent(s) one or more non-hydrolyzable groups, independently of eachother, represent a group selected from: a C1-C20 alkyl group or C3-C10cycloalkyl group substituted with one or more epoxy group(s), said epoxygroup being mono, di, tri or tetravalent; a glycidoxy group; a C1-C20alkyl group substituted with a glycidoxy group; a vinyl group (CH2═CH—);a C1-C20 alkyl group substituted with a vinyl group (CH2═CH—); a C1-C20alkyl group substituted with a primary amine and/or a secondary amineand/or a tertiary amine; a primary amine; a secondary amine; a tertiaryamine; a C1-C20 alkyl group substituted with a thiol group; a thiolgroup; a urea group; a C1-C20 alkyl group substituted with a urea group;an isocyanate group; and a C1-C20 alkyl group substituted with anisocyanate group, and in that at least one group selected from R1, R2and R3 represents, as the hydrolyzable group, a C1-C10 alkoxy group; aC3-C10 cycloalkyloxy group; a C5-C10 aryloxy group or a Cl-05 acyloxygroup.
 7. A binder composition according to claim 5, wherein the motifR₄—(SiR₁R₂R₃) of the organosilane oligomer with formula (I) is selectedfrom a list (IIa): gamma-glycidoxypropyltrimethoxysilane;gamma-glycidoxypropyltriethoxysilane; gamma-glycidoxypropyl;methyldimethoxysilane; and gamma-glycidoxypropylmethyldiethoxysilane. 8.A binder composition according to claim 7, wherein the motifR₄—(SiR₁R₂R₃) of the organosilane oligomer with formula (I) is selectedfrom a list (IIb): beta-(3,4-epoxycyclohexyl)-ethyl trimethoxysiloxane;beta-(3,4-epoxycyclohexyl)-ethyl methyl dimethoxysilane,beta-(3,4-epoxycyclohexyl)-ethyl methyl diethoxysilane; andbeta-(3,4-epoxycyclohexyl)-ethyl triethoxysilane.
 9. A bindercomposition according to claim 1, wherein the hydrolyzed organosilaneoligomer represents in the range 5% to 30% by weight of the total dryweight of said binder composition.
 10. A binder composition according toclaim 1, wherein said binder composition comprises an acidic catalystselected from the group constituted by p-toluene sulfonic acid,phosphoric acid, boric acid, acetic acid, and mixtures thereof.
 11. Akit for a binder composition according to claim 1, wherein said kitcomprises a part A having a pH of less than 6 constituted by an aqueouscomposition comprising a hydrolyzed organosilane oligomer and a part Bcomprising particles of at least one metal oxide and at least onemetallic phosphate, the proportion by weight of particles of at leastone metal oxide relative to the total dry weight of parts A and B addedtogether being greater than or equal to 75%.
 12. A kit according toclaim 11, wherein part A comprises an organosilane oligomer having thefollowing formula (I), [R₄—(SiR₁R₂R₃)]_(n), in which n is an integerwith 2≦n≦100 and R4 is a non-hydrolyzable group, and at least one groupfrom R1, R2, and R3 is a hydrolyzable group, at least one metallicphosphate selected from the group constituted by zinc phosphate(Zn₃(PO₄)₂), manganese phosphate (Mn₃(PO₄)₂), aluminum phosphate(AlPO₄), aluminum tripolyphosphate (Al₅(P₃O₁₀)₃), aluminum and zincphosphate, and mixtures thereof and particles of at least one metaloxide selected from the group constituted by aluminum oxide, zinc oxide,a mixed zinc-magnesium oxide, a mixed aluminum-zinc oxide, and mixturesthereof.
 13. Use of the binder composition according to claim 1 informing a sacrificial corrosion-protective coating on at least onesurface portion of a support.
 14. Use according to claim 13, wherein thesupport is formed from a material selected from metals, metal alloys andcomposite materials comprising a metal or a metal alloy, having anelectrical surface resistivity of less than 1 ohm/square.
 15. A methodof manufacturing and applying a sacrificial corrosion-protective coatingto at least one surface portion of a support using the compositionaccording to claim 1, comprising the following steps in succession: (i)a step of supplying and preparing at least one surface portion of asupport formed from metal or a metal alloy; (ii) a step of applying theaqueous binder composition according to claim 1 in order to form a moistlayer of film on at least said surface portion; (iii) a drying step toevaporate the water and allow a film to be formed at a temperature inthe range 60° C. to 90° C. for at least 5 min. (vi) a final step ofannealing said film obtained at the end of step (iii) at a temperaturegreater than or equal to 250° C. for at least 30 min; (vii) a step offinal compacting of said at least one surface portion coated with saidsacrificial corrosion-protective film so as to form a sacrificialcorrosion-protective coating, preferably with an electrical surfaceresistivity of less than 1 ohm/square.
 16. A method according to claim15, wherein it comprise a step (iv) comprising, repeating steps (ii) and(iii) until a film with a predetermined thickness is obtained.
 17. Amethod according to claim 15, wherein it comprise a step (v) comprisingafter each drying step (iii) with the exception of the last drying step(iii), a step of intermediate annealing and/or a step of intermediatecompacting of the film is/are applied;
 18. A manufacturing methodaccording to claim 15, wherein the preparation step (i) comprises a stepof sanding said at least one surface portion such that said at least onesurface portion has a rough surface, with a surface roughness of lessthan 100 μm.
 19. A support formed from a material selected from metals,metal alloys and composite materials comprising a metal or a metalalloy, with at least a portion of a surface being coated with asacrificial corrosion-protective coating obtained by carrying out themethod in accordance with claim 15 and comprising metallic particles,silica and phosphorus, said coating comprising less than 10% by weightrelative to its total weight, of a hydrocarbon residue, and wherein saidcoating is free of chromium compounds.
 20. A support according to claim19, wherein said support has an electrical surface resistivity of lessthan 1 ohm/square.